A thermosetting resin composition include a liquid epoxy resin, a solid epoxy resin, a semisolid epoxy resin, an epoxy curing agent, and a filler. The liquid epoxy resin is liquid at 20° C. and has at least two epoxy groups in a molecule. A solid epoxy resin is solid at 40° C. and has at least three epoxy groups in a molecule. A semisolid epoxy resin is solid at 20° C. and liquid at 40° C. and has at least two epoxy groups in a molecule. A ratio of mass of the liquid epoxy resin to a sum of mass of the solid epoxy resin and mass of the semisolid epoxy resin is about 1:1 to about 1:10, and a ratio of the mass of the solid epoxy resin to the mass of the semisolid epoxy resin is about 1:0.5 to about 1:2.